In this colloquium I will give an observational overview of the history and status quo of lithium abundance determination in un-evolved stars from solar to the lowest metallicities, and their connection to Big Bang nucleosynthesis. 7Li spectroscopy now encompasses samples of hundreds of thousands of stars, largely thanks to multi-object spectrographs FLAMES/VLT and HERMES/AAT, and corresponding dedicated Galactic Archaeology surveys. The rapidly-growing observational data sets have sparked development of new efficient and automated spectroscopic analysis techniques, with clever optimisation algorithms that also incorporate Gaia data.
lithium problems is improved models of stellar atmospheres and interiors. Credits: Karin Lind, Davide De Martin.
6Li spectroscopy is still limited to a small, but ever increasing, sample of bright stars, with the best data that 8-10 m telescopes and the highest resolution instruments can provide. The lighter isotope, on the other hand, strongly challenges the modelling of the Li resonance line, properly accounting for the Doppler shifts induced by convective motions and the departures from LTE of the atomic level populations. I will review how the observational field has developed since the discovery of the Spite plateau and argue that today, the lithium abundance measurements of un-evolved stars favour "stellar solutions" to the cosmological problems.